When she finishes, Vincent, still raven haired and nearly wrinkle free at 49, stares at her for several seconds.

“I don’t remember any of them,’’ he says.

Alzheimer’s has recently quickened its devastating pace, snatching from Vincent more social skills and abilities than it had since his diagnosis three years earlier. He has a form of the disease that strikes at a young age.

Gone in the latest slide is the easy back and forth of conversation, the ability to sort and price products at the family’s Westminster grocery store that he once ran, and his recall of words, and sometimes entire conversations, from a few minutes earlier. Often he hovers, almost childlike, looking for direction in everyday tasks such as serving salad from a bowl to a dinner plate.

When Vincent shoveled his driveway after the snowstorm last month, he inexplicably walked dozens of yards to the backyard to empty each scoop, instead of simply tossing the snow to the side.

As the disease accelerates, Vincent’s family treasures all the more the bedrock pieces of his personality that remain - his optimism, his gentle nature, and especially his boyish humor.

“If I didn’t have Alzheimer’s,’’ Vincent confided after completing the memory-testing session, “that would have been a blast.’’

Moments like this remind his family that much of what makes Bruce Bruce is still there. Even though he is no longer able to make decisions, much of the family’s life continues to orbit around him.

Vincent and his family, who have allowed the Globe to chronicle their lives during the past year, have spent many hours championing Alzheimer’s research, walking to raise money, speaking at public forums, and traveling to Washington to lobby lawmakers.

He also enrolled in an international study that is tracking families, like the Vincents, who are plagued by a rare, inherited form of Alzheimer’s that usually starts in one’s 40s and 50s.

Dr. Reisa Sperling, a Brigham and Women’s Hospital neurologist who leads the Boston arm of the study, said Vincent’s recent steep decline is mirrored in his latest test results.

“I feel like we are in this terrible race,’’ Sperling said. “If he continues to decline at this rate, he will be too impaired to be in drug trials by the time he reaches 50’’ in May.

Federal regulators typically do not allow volunteers under age 50 into Alzheimer’s drug trials because evidence suggests they may be more vulnerable to serious side effects, Sperling said. And pharmaceutical companies are focused on creating drugs for a larger market - the nearly 16 million Americans who are projected to develop the much more common later-onset form of the disease by 2050.

Current medications cannot cure Alzheimer’s or even stop it from progressing, though they may help in easing some symptoms, such as memory loss, for a limited time. Vincent took one for three years, and after it stopped helping, recently switched to another.

Despite much progress in understanding Alzheimer’s, scientists are still stymied by basic questions. They don’t know why patients with the inherited form of the disease seem to initially have a long period when their symptoms are stable, and then experience a rapid decline.

It may be that younger minds have more resilience against the buildup of sticky clumps of abnormal proteins in the brains of Alzheimer’s patients, Sperling said. But it’s not clear whether these clumps are a cause of the disease or a byproduct.

‘We are just winging it’

The 60-hour weeks Bruce Vincent relished working in the family grocery store just two years ago have dwindled to three-hour days, three days a week.

About a year ago, he turned over management of the store to his son Brian but still worked every day, helping stock shelves and break down boxes. Now he is often confused by tasks more complicated than sweeping the store’s parking lot, picking up the mail, or taking out the trash.

Cindy Vincent, his high school sweetheart and wife of 30 years, is taking more time off from her gift shop to be with him, but Bruce is home alone sometimes. She has left him notes with tasks - pick blueberries, make another pot of coffee, sweep the garage - but she has run out of ideas to keep him busy and worries that he needs more meaningful activities to hold boredom and depression at bay.

“We are just winging it,’’ she said. “He often apologizes to me that his disease affects my life so greatly, and that breaks my heart. He still worries more about other people than himself.’’

A few months ago, she sent an e-mail to their neighbor, Jennifer Shenk, who edits an online magazine in Westminster, the Community Vine, and knows just about everyone in town. Vincent was seeking advice about places her husband might be able to volunteer.

Instead, Shenk suggested that the volunteer concept might work well in reverse.

“I think there are people in town who would happily volunteer to spend time with him,’’ Shenk said later.

Vincent is a Westminster fixture, known not only as the town grocer, but as one of the first to step forward with donations and volunteer in community projects. He is not comfortable, however, with the idea of now having to rely on others.

“I don’t need someone to take care of me,’’ he said when his wife first broached the topic this summer.

She has discreetly kept up the search for a suitable activity into the fall.

“He needs routine to keep things straight,’’ Cindy Vincent said.

Bruce Vincent doesn’t see what is so apparent to his family - that his abilities to converse, reason, and participate in everyday life have significantly diminished.

“I don’t see any differences except for maybe I’m missing a word here or there,’’ he said.

It’s not unusual for people at this stage of the disease to lack perspective about what’s happening to them, said Nicole McGurin, who manages programs, including the support group that Bruce Vincent attends, at the Alzheimer’s Association of Massachusetts and New Hampshire.

One result is that Alzheimer’s patients can develop quirky - and often futile - coping mechanisms.

Vincent carries a worn, folded piece of green paper in his wallet. On it are written four words - canoe, hotel, apple, piano.

When he was first diagnosed with Alzheimer’s, those four words were included in a memory test that had stumped him. So he created a memory aid using the first letter of each word to form another - chap - to help him the next time he took the test. Then he started forgetting what each of the letters in “chap’’ stood for, and wrote the words down.

“I’m trying to pull a fast one on the doctor,’’ Vincent confided as he proudly displayed the cheat sheet.

It’s easy for families like the Vincents to be overwhelmed by the losses and overlook that the essence of the person remains, said Kathleen Rusnak, a Greenfield-based psychologist and Lutheran pastor who counsels patients and families.

Her 82-year-old mother had Alzheimer’s, and in the weeks before her death in August, the former beautician was so disoriented, she didn’t remember where she was born, what state she was in, or sometimes recognize her own daughter. But she was still meticulous about her appearance.

“The day before she died, she put her own lipstick on,’’ Rusnak said. “Despite everything that she couldn’t remember, she was aware of beauty and smell and touch, and what she looked like.’’

Inheriting the disease

Brian Vincent wanted to know if, as he puts it, his life is “half over.’’

The three Vincent children - Brian, Jeff, 28, and Danielle, 21 - each stand a 50 percent chance of inheriting from their father any one of three gene mutations believed responsible for causing Alzheimer’s to start at an early age.

Only about 2 percent of the estimated 5.4 million Americans with Alzheimer’s have this type of the disease. But in these families, it can cut a destructive path through generations.

Alzheimer’s claimed Bruce Vincent’s mother and grandfather, both in their 50s, and Bruce’s great grandfather also died young, at 56, with an unknown dementia.

Shortly before his 27th birthday in September, Brian attended a counseling session before having blood drawn for the test to determine whether he carries any of the mutated genes.

It’s the age, he noted, when “all the rock stars die, like Janis Joplin, Jimi Hendrix, and Amy Winehouse.’’

Counselors told him that some people have committed suicide after learning they have the genes. Others who tested negative were wracked with guilt when a sibling tested positive.

“You can get treated differently by people if they know you are going to have a shortened life,’’ Brian Vincent said.

He decided to put the testing on hold.

Instead, he enrolled in the same international study that his father entered that tracks changes over time in the blood, brain, and spinal fluid of families that carry the rare gene mutations. The study tests for the genes, but does not reveal the outcome to participants.

Researchers hope to translate brain and blood changes they find in these families into a test that would screen for the more common form of Alzheimer’s. Currently, none exists. A reliable test might someday enable physicians to prevent or delay dementia with drugs or other therapies, in much the way they prescribe cholesterol-lowering drugs to stave off heart disease.

Brian’s older brother, Jeff Vincent, a Holden police officer, has no interest in knowing whether he carries the disease-causing Alzheimer’s gene. What’s the point of living with the dread, he says, if there’s no treatment.

But Jeff’s wife, Rebecca, who is completing her master’s degree in elementary education, knows they will confront the decision about testing when they start a family. She wants to know if their children would have a risk of inheriting an Alzheimer’s gene.

The couple, married three summers ago, had planned to wait a while for children, but Rebecca is feeling a growing urgency as her father-in-law declines.

“Part of me wants to start a family now because it would completely break my heart if my children didn’t know their grandfather,’’ she said. Having children sooner would also allow them more years with their father if it turns out that he, too, develops Alzheimer’s, she said.

“But at the same time, I know it’s not wise to have children just because of that,’’ Rebecca said. “I can’t make decisions out of fear.’’

What about the future?

In late September, Bruce and Cindy Vincent were invited to speak to first-year medical students at the University of Massachusetts Medical School.

For most of the hourlong session, Bruce Vincent sat quietly and often expressionless in the center of the amphitheater, flanked by his wife and Nicole McGurin, the program manager from the Alzheimer’s Association, who moderated the session.

McGurin described her organization’s family support services, and Cindy Vincent told the students about her husband’s family history, about his diagnosis, and how life has changed for them since then.

Next, it was the students’ turn.

Bruce Vincent did his best to answer their questions, but often deflected queries with his trademark humor when he was floundering.

“That’s way too much information for someone with Alzheimer’s,’’ he said, after one student asked a detailed question about his family history.

Are there moments of clarity and moments of confusion, another student asked him or is it a gradual change?

“Sometimes you get like a panic attack, when you are not sure what to do,’’ Vincent answered.

“What I do is, I physically, actively take myself four steps back and I just wait, and I let that clear,’’ he said.

Cindy Vincent offered more details to fill in the gaps.

The couple will be driving in the car and a song will come on the radio that they haven’t heard in 20, 25 years, she said. And her husband will sing along, remembering every word, every guitar riff, every note.

“He knows all of that stuff, but he won’t remember what he had for breakfast this morning,’’ she said. “It’s those long-ago memories that he’s still very good with.’’

In the pause that followed, Bruce Vincent looked at his wife and then said to the class: “I had Raisin Bran.’’

The students erupted in laughter.

They asked about the family’s health insurance and whether it covers his growing medical expenses. It has, so far, Cindy Vincent said.

And what about the future, another asked. Have you made any changes to your house to make life easier as your husband’s disease progresses?

Silence.

Cindy Vincent took a deep breath and looked at her husband.

She then described the strategy shared by another woman in the support group she attends at the Alzheimer’s Association.

“Her husband would get up in the middle of the night and wander,’’ Cindy Vincent said.

As she spoke, her husband looked down at the floor.

The woman started tying a scarf around her leg and would loop it around her husband’s ankle in bed at night, Cindy Vincent said.

“It would wake her up so that she would know if he was getting out of bed, because he actually got outside of the house one night,’’ she said.

“We have not had to make any of those kinds of changes,’’ she said, “yet.’’